1. Field of the Invention
The present invention relates to an aluminum alloy member and a method of producing the aluminum alloy member. More particularly, the present invention relates to an aluminum alloy member suitable for a piston, cylinder, or the like of an internal combustion engine, requiring high wear resistance as well as high mechanical strength, and a method of producing the aluminum alloy member.
2. Description of Background Art
An internal combustion engine for a vehicle is requires high mechanical strength, light weight, a low thermal expansion coefficient, and the like. To meet such requirements, main members of an internal combustion engine have been formed from an aluminum alloy by casting. A member having a sliding plane, such as a piston or a cylinder, however, is required to have high wear resistance as well as high mechanical strength and the like. To meet such requirements, for example, a cylinder liner made from cast iron has been press-fitted to a piston sliding plane of a cylinder block, or a sliding plane has been subjected to hard alumite treatment.
The use of the cylinder liner has a problem in complicating the production steps thereof and the recycling steps thereof, and the hard alumite treatment has a problem in degrading the dimensional accuracy of the sliding plane. To solve these problems, Japanese Patent Laid-open No. Hei 2-104465 discloses a technique, in which a piston or a cylinder is produced by casting an aluminum-silicon based alloy material having a hyper-eutectic composition containing 15 to 30 wt % of silicon, and a sliding plane of the piston or cylinder is polished to expose primary crystal silicon grains from the exposed plane, thereby improving the wear resistance of the sliding plane of the piston or cylinder.
The above-described technique has a problem. Since the primary crystal silicon grains have excellent wear resistance but have poor machinability such as the mechanical cutting characteristics, it takes a long time to machine the member formed by casting, thus resulting in an increase in the cost of manufacturing.
An object of the present invention is to solve the above-described problems of the prior art, and to provide an aluminum alloy member having high machinability while keeping sufficient mechanical strength and sufficient wear resistance, and a method of producing the aluminum alloy member.
To achieve the above object, the present invention provides the following aluminum alloy member and method of producing the aluminum alloy member.
(1) The aluminum alloy member, which is formed from an aluminum-silicon alloy by casting, includes eutectic silicon grains that are exposed from part of an exposed plane of the aluminum alloy member.
(2) The method of producing an aluminum alloy member, which is formed from an aluminum-silicon alloy, includes the steps of: casting an aluminum-silicon alloy having an eutectic composition or a hypo-eutectic composition, to form an aluminum alloy raw material; machining the surface of the aluminum alloy raw material formed by casting; etching the machined surface, to expose eutectic silicon grains therefrom; and forming a coating layer on the surface from which the eutectic silicon grains are exposed.
According to the aluminum alloy member having the feature (1), since eutectic silicon grains, which have a machinability higher than that of primary crystal silicon grains while keeping a sufficient wear resistance, are exposed from a sliding plane, it is possible to improve the machinability of the aluminum alloy member while keeping a sufficient wear resistance thereof.
According to the production method having the feature (2), since eutectic silicon grains, which have a machinability higher than that of primary crystal silicon grains while keeping a sufficient wear resistance, are exposed from a sliding plane, it is possible to improve the wear resistance of the aluminum alloy member.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.